This invention generally relates to methods and apparatus for manufacturing slider-operated flexible zippers for use in reclosable pouches, bags or other packages of the type in which material, such as foodstuff and detergent, are stored.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened. To gain acceptance as a primary package for foodstuffs, it is virtually mandatory that the package exhibit some form of tamper evidence to protect the consumer and maintain the wholesomeness of the contained product. In addition, in many cases it is necessary that food product be hermetically packaged. This may readily be accomplished by forming a plastic bag of a film having the appropriate barrier properties. However, where the bag is provided with a zipper, a problem arises in properly sealing the bag at the opening to be closed by the zipper, since the zipper itself does not provide a hermetic seal.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies often include a plastic zipper and a slider. Typically, the plastic zippers include a pair of interlockable fastener elements, or profiles, that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc. Reclosable bags having slider-operated zippers are generally more desirable to consumers than bags having zippers without sliders because the slider eliminates the need for the consumer to align the interlockable zipper profiles before causing those profiles to engage.
Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures, portions of which form a fulcrum about which the profiled structures may be pivoted out of engagement when lower edges of the bases are forced towards each other.
One of the important features of such reclosable fastener assemblies is the end stop, which prevents the slider from falling off when the slider reaches the end of the fastener. A slider end stop is provided on each end of the zipper. End stops have taken on various configurations, such as, for example, riveted end clamps such as those described in U.S. Pat. Nos. 5,067,208 and 5,161,286; transverse end stops made from molten material of the fastener strips, as described in U.S. Pat. No. 5,088,971; reciprocating anvils, as described in U.S. Pat. No. 5,131,121; tubular end stops, as described in U.S. Pat. No. 5,405,478; a window structure combined with sealed zipper ends, as described in U.S. Pat. No. 5,442,837; or plastic end clips fused to the zipper as described in U.S. Pat. No. 5,448,807.
U.S. Pat. No. 5,950,285 discloses a reclosable bag having end stops that prevent a slider from moving beyond the end of the zipper when the slider reaches either the closed or fully open position. The end stops are formed from the material of the zipper profiles and “rise vertically” from the zipper to block and prevent further movement of the slider. The end stops are formed by first aligning together the opposing profiles at an end stop area proximate to an end of the bag, and then fusing the zipper profiles at the end stop area to provide a vertical structure for preventing movement of the slider past the ends of the zipper, while at the same time keeping the base of the profiles intact so that the slider cannot lift off of the zipper in the parked position. Preferably, the profiles are fused by directing ultrasonic energy to the end stop areas.
The slider end stop must be designed to withstand the force applied by a consumer during normal use. More specifically, as the consumer pulls the slider to either end of the zipper, the end stop should not bend, fold, collapse or otherwise lose its ability to stop the slider when the slider is pressed against the end stop with the pulling force being exerted by the consumer. The level of force at which the slider overcomes the end stop and slides off the end of the zipper is termed “the pull-off force.” It is desirable to test the pull-off resistance of end stops on slider-operated zippers during package manufacturing and to remove packages having defective slider end stops or even shut down the production line so that the end stop forming station can be inspected and the source of the defects evaluated.
As previously described, it is also desirable in many applications to provide means for hermetically sealing the zipper of a reclosable package. There are many known ways of providing a hermetic seal. In one type of reclosable package, the profiled closure members are connected by a membrane that is disposed on the product side of the zipper with the ends of the membrane captured in the side seals of the package. A line of weakening, such as a capped line of perforations of the type disclosed in U.S. Pat. No. 5,023,122, is provided in the zipper membrane. The capped line of perforations or other line of weakening weakens the zipper membrane so that it may be readily ruptured, without detracting from the barrier property of the zipper flange until rupturing actually occurs.
In another type of reclosable package, each zipper half has a respective extension flange depending from and connected to the respective profiled closure members. Typically the upper edges of the front and rear walls of the package are heat sealed to the respective zipper flanges to attach the zipper to the package. The zipper is then hermetically sealed by placing a layer of peel seal material between the opposing zipper flanges along the full length of the zipper and then activating the peel seal by application of heat and pressure. For example, it is known to use a continuous band sealing machine to activate a peel seal.
It is further known to manufacture pouches with slider-operated zippers and to sell those pre-made pouches to a converter, who then fills and seals the pouches. Many converters of pre-made pouches having slider-operated zippers request that the pouches be delivered with the sliders in the open position. The pouches are then filled by hand and placed on a conveyor that takes the filled pouches to a continuous band sealing unit. The band sealer will activate the peel seal layer. There is a need for a device for closing the slider-operated zipper prior to shipment of the filled pouch.